Crack Paths 2006

Crack growth simulation by B E Mfor SEN-specimens

undergoing torsion or bending loading

R. Citarella1, F.-G. Buchholz2

1 Department of Mechanical Engineering, University of Salerno, via Ponte don Melillo 1,

Fisciano (Salerno), ITALY,rcitarella@unisa.it

2 Institute of Applied Mechanics, University of Paderborn, Paderborn, G E R M A N Y

ABSTRACT.In this paper the rather complex 3D fatigue crack growth behavior in

3PB-specimens or in cantilever beam specimens undergoing respectively bending or

torsion loading, with inclined planes for the initial crack, is investigated by the aid of the

B E Mprogram BEASY. Mixed mode conditions along the crack edge are characterized.

The stress intensity factors (SIFs) are determined using the crack opening displacement

method (COD)and the crack growth direction is computed by the minimumstrain energy

density criterion. It will be shown that the computationally simulated results of fatigue

crack growth in the Boundary Element (BE) model of the specimen are in good

agreement with experimental findings for the development of the spatially twisted or

twisted and warped crack faces in the real laboratory test-specimens. In particular, the

comparisons with experimental findings are related to the evolving crack shape. The

B E Mresults are also compared with F E Mresults, for which the SIFs are computed by

the virtual crack closure integral (VCCI)-method and strain energy release rates

(SERRs) and for the evolving 3D crack shape the ´1 criterion is adopted as fracture

criterion. Consequently, also for these cases with a rather complex 3D crack growth

behaviour, the functionality of the BEASYprogramme and the validity of the proposed

3D fracture criterion can be stated.

I N T R O D U C T I O N

A number of fracture criteria for predicting the initiation and the direction of fatigue crack

growth under mixed-mode I and II crack tip loading conditions are well established. But

for the corresponding 3D case this can not be stated, because only a few 3D fracture

criteria have been proposed so far and besides some theoretical and computational

investigations there is only very limited experimental work available on which they could

be based and proved. In this paper detailed results of two computational 3Dfatigue crack

growth simulations will be presented with reference to [1, 2]. The simulations are based

on a MinimumStrain Energy Density criterion (in the following we will use the acronym

MSED)[3] and on the Dual Boundary Element Method (DBEM)as implemented in the

commercial BE-programmeBEASY.The specimens under investigation are single edge

notched (SEN) specimens with an inclined crack or notch plane and subject to three point